CHAPTER XV. 



OLD RED SYSTEM (continued). 



Trap-Dykes in the Old Red Sandstone ; Mineral Veins; Dislocations ; Outliers ; 



Agricultural Characters of the System. 



TWO examples only are yet known of trap rocks within the wide area occupied by 

 the Old Red Sandstone : the one at Bartestree near Hereford is marked in Mr. 

 Greenough's map ; the other, at Brockhill, on the left bank of the river Teme in Wor- 

 cestershire, has not previously been noticed. 



The Bartestree or Hereford trap dyke extends from west-south-west to east-north- 

 east, as defined by the direction of its walls in the principal quarry called Low's Hill, 

 where the stone has long been worked for the use of the roads. (See Map.) It is cut 

 into to a depth of fifty feet, and a length of about a hundred and twenty feet. This 

 excavated space is nearly sixty feet wide at its entrance, but the trap diminishes to 

 about twenty feet in width at the extreme end of the quarry. The prevailing variety 

 of the trap is a highly crystalline greenstone, made up of hornblende, olivine, and 

 felspar. The central mass, having more or less the large spheroidal form, is hard and 

 compact, with more hornblende than felspar, the mixture of these minerals being ex- 

 ceedingly intimate. Other portions of the dyke, particularly those which are near the 

 sides, assume a prismatic form, the ends of the prisms directed towards the walls, and 



